Susac syndrome misdiagnosed as multiple sclerosis with exacerbation by interferon beta therapy

Susac syndrome is a rare autoimmune disorder characterised by the clinical triad of encephalopathy, retinopathy (branch retinal artery occlusions) and hearing loss. The diagnosis of Susac syndrome may be difficult initially, and it is not uncommon for patients with Susac syndrome to be misdiagnosed with multiple sclerosis. In this case report, we describe a patient who was diagnosed as having multiple sclerosis for three years, with further deterioration after starting treatment with interferon beta-1a. The patient had the triad of encephalopathy, branch retinal artery occlusions and sensorineural hearing loss. She had the classic magnetic resonance imaging appearance, with normal magnetic resonance imaging of the spinal cord and absence of oligoclonal bands in the cerebrospinal fluid. Our patient responded well to treatment with a combination therapy and discontinuation of interferon beta-1a. Our observations raise awareness about the importance of the early and correct diagnosis of Susac syndrome, which usually affects young patients, with an excellent prognosis if treated aggressively at an early stage of the disease. Susac syndrome is underdiagnosed and is not uncommonly misdiagnosed as multiple sclerosis. Susac syndrome is a great mimicker of multiple sclerosis, and establishing diagnostic criteria for this syndrome is very useful. In any patient presenting with a progressive disabling neurological disorder associated with callosal lesions and/or hearing loss, and/or visual loss especially in women, Susac syndrome should be suspected.